PSI - Issue 8

Antonio Mancino et al. / Procedia Structural Integrity 8 (2018) 526–538 Mancino A. et al. / Structural Integrity Procedia 00 (2017) 000 – 000

528

3

quality of the composites (usually obtained without proper cure and/or post-cure processes) and the low volume fiber concentration (commonly lower than 20%). In fact, as it is demonstrated in the present work, using natural fibers (never perfectly straight), in general high fiber concentrations and good quality can be obtained only by applying a suitable post-cure process characterized by the application of appropriate molding pressure

2.1. Green epoxy matrix

In accordance with the experimental results obtained in (Zuccarello and Scaffaro (2017)), a green epoxy resin with IHN type hardener (see technical data sheet reported in the reference list), produced by the Entropy Resin Inc. (CA) USA and called SUPERSAP CNR, has been considered. As widely shown in Zuccarello and Scaffaro (2017), this is an environmentally friendly matrix with mechanical properties comparable to those of a common epoxy resin obtained from the petrochemical industry. Systematic pull-out tests on single fiber have also shown that such a green matrix has good compatibility with optimized agave fibers, with a relatively high adhesion index values, not less than 0.73 for fibers without any surface treatment (see references by Zuccarello and Scaffaro (2017)). Fig. 1 shows the result of a specific tensile test performed on the particular batch of matrix used in this work, by means of a tensile test specimens prepared in accordance with the ASTM D638 – 14.

Fig. 1. Tensile test on the green epoxy matrix used in this work.

It is observed how this matrix exhibits an initial linear elastic behavior (up to a stress of about 40 MPa and strain about 2%) followed by a limited elasto-plastic phase until the ultimate stress  m,R =50 MPa, that occurs at the ultimate strain  m,R =3%. The Young modulus is E m =2.58 GPa. The shear behavior, determined by means of Iosipescu shear tests, is governed by a larger plastic phase with an ultimate shear stress  m,R =35 MPa and by a shear modulus G m =1.20 GPa (see Table 1).

Table 1. Properties of the green epoxy resin considered in this study.  m,R [MPa]  m,R [%]  m [GPa]

G m [GPa]

 m,R [MPa]

 m,R [%]

50

3

2.58

35

5

1.20